Conventional techniques for detecting obscured targets employ some form of xe2x80x9chuman intelligencexe2x80x9d where xe2x80x9ca priorixe2x80x9d information is gathered over a period of time by one of the intelligence agencies. If a threat is detected as a result of these intelligence gathering procedures, military or paramilitary forces are often employed at the risk of injury. In extreme cases even loss of life may be incurred. Also, expensive equipment may become severely damaged or unrecoverable.
On the technology forefront, advanced Automatic Target Recognition (ATR) research in the last decade or so has been focused on developing Synthetic Aperture Radar (SAR) and Electro-Optics (EO) along with other imaging technologies for specific reconnaissance and surveillance platforms. Recent advances have led to a limited number of automated techniques for detecting targets in open terrain and over a limited number of benign conditions. For situations that require the detection of obscured targets, recent initiatives such as development efforts for Foliage Penetration (FP) and Ground Penetrating Radar (GPR) show promise as future technologies to detect targets within forest clutter and obtain signal information from underground facilities, respectively. At present, these technologies have a great deal of scope for further development and are not fully mature for even initial implementation. Realistic possibilities for near-term exploitation of these technologies require a considerable amount of human-in-the-loop intervention to combine information from a variety of sources.
In the present invention, a bistatic/multistatic radar system concept is described for purposes of interrogating difficult and obscured targets via the application of low-altitude xe2x80x9csmartxe2x80x9d or xe2x80x9crobotic-typexe2x80x9d unmanned air vehicle (UAV) platforms. A significant aspect of the invention is the formulation of a UAV system concept that implements self-adaptive positional adjustments based on sensed properties of the propagation channel (i.e. phase discontinuities). The present invention adapts the concept of a notational urban environment as illustrated in the sample scene of FIG. 1.
A bistatic/multistatic radar system concept for purposes of interrogating difficult and obscured targets via the application of low-altitude xe2x80x9csmartxe2x80x9d or xe2x80x9crobotic-typexe2x80x9d unmanned air vehicle (UAV) platforms. A significant aspect of the invention is the formulation of a UAV system concept that implements self-adaptive positional adjustments based on sensed properties of the propagation channel (i.e. phase discontinuities).
It is therefore an object of the invention to provide a bistatic/multistatic radar system concept for purposes of interrogating difficult and obscured targets via the application of low-altitude xe2x80x9csmartxe2x80x9d or xe2x80x9crobotic-typexe2x80x9d unmanned air vehicle (UAV) platforms.
It is another object of the invention to provide a bistatic/multistatic radar system concept for purposes of interrogating difficult and obscured targets via the application of low-altitude xe2x80x9csmartxe2x80x9d or xe2x80x9crobotic-typexe2x80x9d unmanned air vehicle (UAV) platforms that implement self-adaptive positional adjustments based on sensed properties of the propagation channel.
It is another object of the invention to provide a bistatic/multistatic radar system concept for purposes of interrogating difficult and obscured targets via the application of low-altitude xe2x80x9csmartxe2x80x9d or xe2x80x9crobotic-typexe2x80x9d unmanned air vehicle (UAV) platforms developed by deriving approximate electromagnetic signal models based on the uniform theory of diffraction.
These and other objects of the invention described in the description, claims and accompanying drawings are achieved by a multi-mode, radar method for detecting targets in urban environments comprising the steps of:
transmitting an electromagnetic signal from a high altitude unmanned air vehicle to an urban environment including between buildings;
receiving by a low altitude unmanned air vehicle a plurality of electromagnetic rays from said electromagnetic signal from said transmitting step, said electromagnetic signal diffracting and reflecting off buildings in said urban environment, an electric field at said low altitude unmanned air vehicle defined as       E    r    =            E      t        ⁢          A      t        ⁢                  ∑                  s          =          1                S            ⁢              xe2x80x83            ⁢                        (                                    ∏                              m                s                                            M                s                                      ⁢                          xe2x80x83                        ⁢                                          A                R                            ⁢                              R                _                                              )                ⁢                  (                                    ∏                              n                s                                            N                s                                      ⁢                          xe2x80x83                        ⁢                                          A                D                            ⁢                              D                _                                              )                ⁢                  exp          ⁡                      (                          -                              jkd                s                                      )                              
where
Er is the received electric field
Et is the transmitted electric field
S is the number of signal paths from transmitter to receiver
{overscore (R)} is the reflection coefficient at Ms reflection points in the s_th signal path
{overscore (D)} is the diffraction coefficient at Ns diffraction points in the s_th signal path
At is the spatial attenuation factor from transmitter to first reflection point
AR is the spatial attenuation factor for reflection points
AD is the spatial attenuation factor for diffraction points
ds is the length of s_th signal path;
compensating for phase deviation in said electromagnetic signal transmitted from said high altitude unmanned air vehicle and received by said low altitude unmanned air vehicle;
determining signal differential path lengths by measuring the phase difference between high altitude unmanned air vehicle electromagnetic signals and electric field phase measurements at said low altitude unmanned air vehicle, said signal differential path lengths indicating an obstruction embedded within said urban environment; and
monitoring said signal differential path lengths and said low altitude unmanned air vehicle converging to a vicinity of said obstruction.